The present invention concerns a composite electrode comprising a bonded body of a conductor such as aluminum and an electroconductive polymer such as a polyaniline, as well as an electric cell using such a composite electrode.
A method of synthesizing an organic polymer by electrolytically oxidizing organic material has been known long since and various polymers have been developed by electrochemically controlling the synthesis of organic polymers.
Particularly, it has been known that polymers obtained by polymerization under electrolytic oxidization such as polypyrrole, polythiophene, polyphenylene, and polyaniline (Polypyrrole in A. F. Dinz, J. Chem. Soc., Chem. Commun., 1975, 635; Polythiophene in Japanese Patent Laid-Open No. 56-47421; Polyphenylene in Electrochem., Acta. 27, 61 (1982); Polyaniline in F. Diaz. J. Electroanal. Chem. 111, 1524 (1980)) have electroconductivities that can range from values corresponding to those of insulators or semiconductors up to those of metals, with the higher conductivities being attainable by doping such polymers with certain impurities. It has also been known that the doping is reversible and accompanies color change. Accordingly, vigorous studies have been made of applications or uses in display elements, photoelectronic conversion elements, switching elements, electrode materials, secondary cells, electromagnetic shielding materials and various kind of sensors.
It is customary to use such polymeric materials in a composite structure, i.e., in combination with other conductors (mainly metals), and aluminum is preferred as the conductor that can be used without impairing the advantageous properties of the polymeric material (reduced weight, thin film-like shape, etc.). Since aluminum is relatively light in weight and excellent in ductility as compared with other metals (Fe, Ni, Cu, etc.) it has been applied generally to those devices and composite materials intending for the reduction of weight and thickness. In addition, they have also been utilized frequently in electrolytic capacitors because of easy formation of oxide films and easy etching, as well as in the fabrication of conductive layers or reflective layers by means of Schottky junction using a gas phase method such as vapor deposition onto various kinds of materials.
The composite body comprising aluminum and polymer has been proposed for various aspects as functional electrodes. The present inventors have heretofore considered that it is preferable to apply electrolytic etching to aluminum production of for composite electrodes comprising a bonded body of aluminum and polymer, in order to obtain close bondability between aluminum and polymer, improvement in the charge collecting efficiency from the polymer and easy removal of oxide layers of aluminum (Japanese Patent Laid-Open No. 61-133,557). However, when electrolytic etching is applied to usual aluminum, although the surface area of the aluminum is increased and the close bondability between aluminum and polymer is improved, it involves a drawback that the mechanical strength of the aluminum is markedly reduced.
In use of a composite electrode comprising the bonded body of aluminum and polymer as a functional electrode in various devices, however ensuring the mechanical strength thereof is one of the items required from the view point of the manufacturing operation and also from the functional view point.